Cisco Systems has started releasing security patches for a critical flaw in Adaptive Security Appliance (ASA) firewalls targeted by an exploit linked to the U.S. National Security Agency.

The exploit, dubbed ExtraBacon, is one of the tools used by a group that the security industry calls the Equation, believed to be a cyberespionage team tied to the NSA.

ExtraBacon was released earlier this month together with other exploits by one or more individuals who use the name Shadow Brokers. The files were provided as a sample of a larger Equation group toolset the Shadow Brokers outfit has put up for auction.

ExtraBacon exploits a buffer overflow vulnerability in the Simple Network Management Protocol (SNMP) implementation from Cisco's ASA software. It allows attackers to remotely execute rogue code on the affected devices, as long as they can send traffic to their SNMP interface. This typically requires being on the same internal network as the targeted devices.

Even though the ExtraBacon exploit was designed to work for versions 8.4(4) and earlier of the ASA software, other researchers demonstrated that it can be modified to also work on newer versions. Cisco confirmed in an advisory that all versions of SNMP in Cisco ASA software contain the flaw.

On Wednesday, the company updated its advisory to announce the availability of patched versions for different Cisco ASA branches, namely 9.1.7(9), 9.5(3), and 9.6.1(11).

Devices using ASA software versions from the 8.x and 7.x branches should be migrated to version 9.1.7(9), according to the vendor. Also, patched releases for the 9.0, 9.2, 9.3, and 9.4 branches are expected Thursday and Friday. These will be 9.0.4(40), 9.2.4(14), 9.3.3(10) and 9.4.3(8).

In addition to ASA software, which is used in different stand-alone devices and security modules for routers and switches, the Cisco Firepower Threat Defense (FTD) Software, the Cisco Firewall Services Module (FWSM), and Cisco PIX Firewalls are also affected by this vulnerability.

Software version 6.0.1(2) was released for Cisco FTD, but Cisco Firewall Service Modules and Cisco PIX Firewalls have reached their end of life, and no patches will be provided for them.

Security researchers have so far established links between the code in the tools leaked by Shadow Brokers and those previously found in the wild and attributed to the Equation group. Furthermore, 14 files leaked by Shadow Brokers contain a 16-character string that NSA operatives are known to have used in their malware and which is listed in an NSA manual leaked by Edward Snowden, The Intercept reported.

There is a second Equation exploit in the Shadow Brokers leak that targets ASA software. It is called EpicBanana and exploits a vulnerability that Cisco claims was patched back in 2011 in version 8.4(3). Nevertheless, the company published a new advisory for the flaw in order to increase its visibility.

A third exploit, BenignCertain, affects legacy Cisco PIX firewalls that are no longer supported. Cisco investigated the exploit and said only versions 6.x and earlier of the PIX software are affected. Users who still have such devices on their networks should make sure they're running software versions 7.0 and later, which are not affected.